Biochemical characterization of a novel glycoside hydrolase family 11 xylanase from Chaetomium sp. suitable for bread making

Improving the inhibitory resistance of xylanase FgXyn11C from Fusarium graminearum to SyXIP-I by site-directed mutagenesis

The aim of this study was to improve the inhibitory resistance of xylanase FgXyn11C from Fusarium graminearum to XIP in cereal flour. Site saturation mutagenesis was performed using computer-aided redesign. Firstly, based on multiple primary structure alignments, the amino acid residues in the active site architecture were identified, and specific residue T144 in the thumb region of FgXyn11C was selected for site-saturation mutagenesis. After screening, FgXyn11CT144F was selected as the best mutant, as it displayed the highest enzymatic activity and resistance simultaneously compared to other mutants. The specific activity of FgXyn11CT144F was 208.8 U/mg and it exhibited complete resistance to SyXIP-I. Compared with the wild-type, FgXyn11CT144F displayed similar activity and the most resistant against SyXIP-I. The optimal temperature and pH of the wild-type and purified FgXyn11CT144F were similar at pH 5.0 and 30 °C. Our findings provided preliminary insight into how the specific residue at position 144 in the thumb region of FgXyn11C influenced the enzymatic properties and interacted with SyXIP-I. The inhibition sensitivity of FgXyn11C was reduced through directed evolution, leading to creation of the mutant enzyme FgXyn11CT144F. The FgXyn11CT144F resistance to SyXIP-I has potential application and can also provide references for engineering other resistant xylanases of the GHF11.

Rice straw as microalgal biofilm bio-carrier: Effects of indigenous microorganisms on rice straw and microalgal biomass production

Microalgal biofilm cultivation is a promising method for efficient microalgae production. However, expensive, difficult-to-obtain and non-durable carriers hinder its up-scaling. This study adopted both sterilized and unsterilized rice straw (RS) as a carrier for the development of microalgal biofilm, with polymethyl methacrylate as control. The biomass production and chemical composition of Chlorella sorokiniana, as well as the microbial community composition during cultivation were examined. The physicochemical properties of RS before and after utilized as carrier were investigated. The biomass productivity of unsterilized RS biofilm exceeded that of suspended culture by 4.85 g m^-2·d^-1. The indigenous microorganisms, mainly fungus, could effectively fixed microalgae to the bio-carrier and enhance its biomass production. They could also degrade RS into dissolved matters for microalgal utilization, leading to the physicochemical properties change of RS in the direction which favored its energy conversion. This study showed that RS can be used effectively as a microalgal biofilm carrier, thus presenting a new possibility for the recycling of rice straw.

Engineering mesophilic GH11 xylanase from Cellulomonas flavigena by rational design of N-terminus substitution

Xylanase, a glycoside hydrolase, is widely used in the food, papermaking, and textile industries; however, most xylanases are inactive at high temperatures. In this study, a xylanase gene, CFXyl3, was cloned from Cellulomonas flavigena and expressed in Escherichia coli BL21 (DE3). To improve the thermostability of xylanase, four hybrid xylanases with enhanced thermostability (designated EcsXyl1–4) were engineered from CFXyl3, guided by primary and 3D structure analyses. The optimal temperature of CFXyl3 was improved by replacing its N-terminus with the corresponding area of SyXyn11P, a xylanase that belongs to the hyperthermostable GH11 family. The optimal temperatures of the hybrid xylanases EcsXyl1–4 were 60, 60, 65, and 85°C, respectively. The optimal temperature of EcsXyl4 was 30 C higher than that of CFXyl3 (55°C) and its melting temperature was 34.5°C higher than that of CFXyl3. After the hydrolysis of beechwood xylan, the main hydrolysates were xylotetraose, xylotriose, and xylobiose; thus, these hybrid xylanases could be applied to prebiotic xylooligosaccharide manufacturing.